This invention relates to electronic test instruments and, more particularly, to electronic instrumentation for signal measurements during tests performed on electrical, electro-optical, opto-electrical, and/or optical systems, subsystems, and associated components. Specifically, the invention is directed to calibration and error correction for electrical-source-to-electro-optical-device impedance mismatch, as well as opto-electrical-device-to-electrical-receiver impedance mismatch, in an electronic test instrument for accurately performing these tests. One embodiment of the invention provides such calibration and error correction for a lightwave component analyzer having at least an internal optical receiver and preferably also having an internal optical source which are selectively connectable by switches configurable by means of an instrument controller for calibration and performance of at least electro-optical and opto-electrical measurements. The switches are arranged in a configurable switch matrix which is connected by the instrument controller in response to selection of a measurement by a user to facilitate calibration of, and error-corrected measurements with, the lightwave component analyzer.
An exemplary use of the invention is in the field of optical and electrical signal measurements in connection with fiber optic systems. With higher bit rates and wider-band modulations becoming prevalent in fiber optic systems, the designers and manufacturers of these systems, as well as subsystems and associated components, need to be able to accurately characterize performance at increasingly higher modulation rates. Some new fiber optic systems now operate at speeds of one GBPS and higher, which are equivalent to RF and low microwave frequencies.
Various test systems have been developed to meet these measurement needs. One such test system is the HP 8702A lightwave component measurement system produced by Hewlett-Packard Company, Network Measurements Division, Santa Rosa, Calif. This system comprises an internal electrical source incorporated into an analyzer for performing electrical calibration and measurements, but the system comprises a discrete optical source and a discrete optical receiver for performing electro-optical (E/0), opto-electrical (0/E), and optical calibration and measurements. This system has the significant advantage that it incorporates a technique for calibrating the test system for performing the desired signal measurements by calibrating the optical source and receiver (or electro-optical and opto-electrical converters) in terms of their modulation (or demodulation) transfer characteristics. However, this system does not calibrate and error-correct E/0 or 0/E test measurements for impedance mismatches between the electrical source and an E/0 device under test or between an 0/E device under test and the electrical receiver. This has resulted in reduced accuracy during testing.